bioRxiv preprint doi: https://doi.org/10.1101/612606; this version posted April 17, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. Defining Escherichia coli as a health-promoting microbe against intestinal Pseudomonas aeruginosa Theodoulakis Christofi1, Stavria Panayidou1, Irini Dieronitou1, Christina Michael1 & Yiorgos Apidianakis1* 1Department of Biological Sciences, University of Cyprus, Nicosia, Cyprus *Corresponding author, email:
[email protected] Abstract Gut microbiota acts as a barrier against intestinal pathogens, but species-specific protection of the host from infection remains relatively unexplored. Taking a Koch’s postulates approach in reverse to define health-promoting microbes we find that Escherichia coli naturally colonizes the gut of healthy mice, but it is depleted from the gut of antibiotic-treated mice, which become susceptible to intestinal colonization by Pseudomonas aeruginosa and concomitant mortality. Reintroduction of fecal bacteria and E. coli establishes a high titer of E. coli in the host intestine and increases defence against P. aeruginosa colonization and mortality. Moreover, diet is relevant in this process because high sugars or dietary fat favours E. coli fermentation to lactic acid and P. aeruginosa growth inhibition. To the contrary, low sugars allow P. aeruginosa to produce the oxidative agent pyocyanin that inhibits E. coli growth. Our results provide an explanation as to why P. aeruginosa doesn’t commonly infect the human gut, despite being a formidable microbe in lung and wound infections.